I will give you an animation to try to simplify what these gentlemen are trying to explain to you. Room treatment is a bit expensive. But if money is no problem then go for it. It does work.
https://www.acs.psu.edu/drussell/Demos/superposition/superposition.html
Two sine waves travelling in opposite directions create a standing wave This is a good example that isn't too hard to understand.
These are the finest. Read thoroughly and check the animations.
https://www.acousticsciences.com/high-end-audio/bass-trapsAnd a mechanical solution that is not as expensive, but is a good bang for the buck is to minimize the resonance by decoupling. Again not perfect but good for less money.
https://isoacoustics.com/Good luck and don't get too aggravated, rooms are the biggest challenge to tame. The information is available on line, and there is many DIY projects that can be found on YouTube that work, and are cheaper.